The present invention relates to equipment and methods for the photolithography of photoresist-coated substrates such as those used for high-density circuit patterns.
The exposure of flexible and rigid electronic substrates such as those used for high density circuit patterns is generally performed with both the substrate and the photo tool, artwork, or mask in a horizontal position by a single exposure from a vertically directed collimated light beam. Conventional substrate exposure systems use various configurations of belts, suction cups, rollers and flipping mechanisms to move the substrates through the imaging process. However, for a number of reasons, such methods do not work well for flexible substrate, which are often difficult to handle and susceptible to warping. Such warping makes the accurate photolithography of the substrate virtually impossible and handling of such substrates unreliable. Another problem is that due to their acute thicknesses, these substrates typically need to be aligned to a precision within a few microns during the imaging process, making accurate and repeatable exposures difficult. Problems with repeatability lead to the frequent rejection of substrates for failing to meet minimum quality control standards.
While a number of manufacturing techniques have been developed in attempts to avoid these problems, such techniques have proven to be difficult and costly to implement. Moreover, current methods do not generally permit the quick and accurate exposure of a large number of substrates in an automated fashion.
With regard to the problem of warped substrates, thin substrates are often introduced to the machine in a warped state or are warped during the imaging process because of other upstream processes. The increased temperatures often cause the substrates to deform, making it difficult to maintain precise alignment of the substrates with the mask during the imaging process. These problems in handling make conventional exposure methods for such substrates costly, time consuming and unreliable.
Yet another difficulty with existing methods for exposing substrates has been that such exposures must generally be done in a clean room so as to avoid contaminating either the mask or the photoresist coating on the substrate with dust or dirt. Because the equipment associated with the exposure of substrates is generally very large, these exposure devices are not very compact and require a lot of space. Moreover, if the equipment is installed in a clean room, any routine maintenance can be difficult and costly due to the steps that must be taken in maintaining the clean room atmosphere.
An improved apparatus and method for exposing a large number of photoresist-coated substrates quickly, reliably and at low cost is desired.
According to the present invention an improved apparatus and method for double-sided imaging of a plurality of substrates is provided. The apparatus includes a first substrate holder comprising at least three extendable chucks, each adapted to hold the substrate. The first substrate holder is mounted about a first axis such that the chucks are capable of rotation about the first axis between at least a first, second and third chuck positions. A first transfer arm is disposed adjacent the first substrate holder and adapted to transfer the substrate to a chuck of the first substrate holder when the chuck is in the first chuck position. A first mask is provided adjacent the chuck in the second chuck position of the first substrate holder.
The apparatus also includes a second substrate holder comprising at least three extendable chucks, each adapted to hold a substrate and mounted about a second axis such that the chucks are capable of rotation about the second axis between at least first, second and third chuck positions. The first chuck position of the second substrate holder is adjacent the third chuck position of the first substrate holder. A second mask is provided adjacent the chuck in the second chuck position of the second substrate holder. At least one radiation source is provided for emitting radiation through the first and second masks toward the chucks in the second chuck position of each of the first and second substrate holders. A second transfer arm is provided adjacent the second substrate holder for transferring a substrate from the third chuck position of the second substrate holder to an out-feed of the apparatus.
In the preferred embodiment the apparatus is automated through the use of a central processing unit (CPU), and most preferably, through the use of a microprocessor. In order to expose a batch of substrates, a first sheet of substrate is driven by rollers of an in-feed conveyor towards an in-feed transfer arm. The substrate is then lifted from the in-feed conveyor and loaded onto a rotating first substrate holder comprising a plurality of extendable chucks rotatable between at least first, second and third chuck positions. The substrate is initially loaded onto a first chuck when it is in the first chuck position. Once loaded, the first chuck of the first substrate holder is rotated from its first position to a second chuck position where the chuck is extended, moving the substrate toward the first mask. A first dieset assembly that holds the first mask is lifted to place the mask in contact with the substrate and a first side of the substrate is exposed with radiation directed through the first mask. After the substrate is exposed, the first chuck of the first substrate holder is rotated to the third chuck position.
In the third position of the first substrate holder, the substrate is transferred from the first chuck of the first substrate holder to an adjoining first chuck of the second substrate holder. Once loaded, the first chuck of the second substrate holder is rotated from its first position to a second chuck position where the chuck is extended, moving the substrate toward the first mask. A second dieset assembly that holds the second mask is lifted to place the mask in contact with the substrate and a second side of the substrate is exposed with radiation directed through the second mask. After the substrate is exposed, the first chuck of the second substrate holder is rotated to the third chuck position. In the third position, the substrate is loaded onto the out-feed transfer arm, which lowers the exposed substrate onto the out-feed conveyor, thus completing the exposure cycle. In preferred embodiments, the present invention may handle up to seven or more substrates simultaneously.